Now that API v2 is gone, what would be a way to get a simple RSS feed of a channel, without v3 API? I'm open to Yahoo Pipes or any workaround that is simpler than creating an application for v3 API if the target is a feed reader. I only need an RSS feed. It was available publicly until now and it can cease any minute now (I think). So why not let access to it without an API key anymore.
At RSS Reader section https://support.google.com/youtube/answer/6098135?hl=en there is an option to export to an OPML file your subscriptions. Then, looking at the contents of the OPML you can extract the feeds, and the structure of each feed is:
So you could generate new feeds from this structure if you know the channel id. This kind of feeds are not getting the "https://youtube.com/devicesupport" error, so I expect they are going to keep working.